Oxide dispersed high purity nickel for use in thermostat metals

ABSTRACT

A composite thermostat metal material characterized by high electrical conductivity, improved resistance to deformation at elevated temperatures, and low cost embodies outer layers of relatively high and relatively low coefficients of thermal expansion respectively, and has an intermediate metal layer of a selected nickel alloy embodying a magnesium oxide constituent.

United States Patent [191 Ornstein et a1.

1 OXIDE DISPERSED HIGH PURITY NICKEL FOR USE IN THERMOSTAT METALS [75] Inventors: Jacob L. Ornstein, Norton; Norman Yarworth, Attleboro, both of Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

22 Filed: July 1, 1974 211 Appl. No.: 484,522

1451 Sept. 2, 1975 3,767,370 10/1973 Ornstein 29/1955 3.788,821 1/1974 Omstein 1 29/1955 3,829,296 8/1974 Charest et a1. 29/1955 3,838,985 10/1974 Omstein 29/1955 Primary ExuminerL. Dewayne Rutledge Assistant Examiner-Arthur J. Steiner Attorney, Agent, or Firm-Russell E. Baumann; John A. Haug; James P. McAndrews [57] ABSTRACT A composite thermostat metal material characterized by high electrical conductivity, improved resistance to deformation at elevated temperatures, and low cost embodies outer layers of relatively high and relatively low coefficients of thermal expansion respectively, and has an intermediate metal layer of a selected nickel alloy embodying a magnesium oxide constituem.

5 Claims, 1 Drawing Figure OXIDE DISPERSED HIGH PURITY NICKEL FOR USE IN THERMOSTAT METALS BACKGROUND AND SUMMARY OF INVENTION The present invention relates generally to thermostat materials and more particularly is directed to an improved multilayer composite thermostat material.

As the usage of thermostat materials for various applications has increased in recent years it has become necessary to provide such materials having a wide vari-' ety of characteristics in order to achieve the desired functions. Accordingly, thermostat materials having a pair of outer layers of metallic material having substantially different coefficients of thermal expansion have been sometimes combined with an additional intermediate layer of metal in order to obtain certain improved characteristics.

In one commonly used thermostat metal, for example, high purity nickel is used as an intermediate shunt layer in a thermostat metal to impart a desired low resistivity to the thermostat metal while not substantially reducing the flexivity thereof. However, certain difficulties arise as a result of using high purity nickel for this purpose because. although the shunt material displays low resistivity, the material has the tendency to soften at comparatively low temperatures. Thermostat metals using such a shunt layer to achieve low composite metal resistivity have been useful only at relatively low temperatures. On the other hand, where other shunt layer materials have been proposed or used in order to achieve high temperature operation, relatively thick shunt layers have been required in order to achieve the desired low resistivity and the use of such relatively thick shunt layers has tended to be expensive and to somewhat reduce flexivity of the thermostat metal.

It is an object of the present invention to provide an improved compositethermostat material having desired characteristics of resistivity .and flexivity and which is suitable for use over a substantially extended temperature range.

It is yet another object of the present invention to provide an improved composite thermostat material which is durable in use, has good corrosion resistance properties, and is relatively economical to fabricate.

Other objects and advantages and details of the composite material provided by this invention appear in the following detail description of preferred embodiments of the material, this description referring to the drawing in which:

The FIGURE is a perspective material of this invention.

Referring to the drawings, a strip of composite thermostat material in accordance with the present invention is indicated by reference numeral 10. As illustrated the composite thermostat material includes a first outer layer 12 of a first preselected metallic alloy having a relatively high coefficient of thermal expansion, a second outer layer 14 of a second preselected metallic alloy having a relatively lower coefficient of thermal expansion with respect to the first preselected material. and an intermediate layer 16.

In fabrication of the composite thermostat material, the first and second outer layers l2, 14 are metallurgically bonded, preferably solid-phase bonded. to the opposed surfaces of this intermediate layer 16, the bonds between the respective metallic layers extending subview of the composite stantially throughout the entire contiguous surfaces of the layers defining the composite material 10. The various layers are'preferably solid-phase bonded together in the manner described, for example, in U.S. Pat. Nos. 2,691 ,8l 5 and 2,753,623. Alternatively, if desired, various other bonding techniques may be utilized for metallurgically bonding the layers together within the scope of the present invention. It may be noted that the thickness of the composite material 10 may vary from approximately 0.001 inch to 0.l00 inch. The illustrated composite thermostat material 10 thus comprises an integral unit adapted to flex in response to temperature changes.

The first and second outer layers 12, 14, as previously indicated, are respectively of materials having a relatively high coefficient of thermal expansion and a relatively lower coefficient of thermal expansion, and are formed from a wide variety of materials compatible with the material of the intermediate layer 16 within the scope of this invention. For example, the first outer layer preferably comprises a material which comprises by weight approximately 22 percent nickel, 3 percent chromium, and the balance iron commonly known as Alloy B which has a coefficient of thermal expansion of approximately X 10" inch per inch per degree Fahrenheit and a resistivity of approximately 460 ohms per circular mil foot. Alternately, a material is utilized in the layer 12 which comprises by weight approximately 72 percent manganese, 18 percent copper, and 10 percent nickel which is commonly known as Alloy P and has a coefficient of thermal expansion of approximately X 10 inch per inch per degree Fahrenheit and a resistivity of l,0l9 ohms per circular mil foot. The second outer layer 14, similarly comprises one of several materials and, for example, preferably comprises a material having a composition by weight of approximately 35 /2 percent to 36/2 percent nickel and the balance iron which is commonly known as lnvar or Alloy l0 and has a coefficient of thermal expansion of approximately 7 X 10 inch per inch per degree Fahrenheit and a resistivity of approximately 484 ohms per circular mil foot. These examples of specific materials comprising the first and second outer layers l2, 14 are purely illustrative and are merely presented as examples of typical, common, commercially available and relatively inexpensive materials which are suitable for use in fabricating a composite thermostat material in accordance with the present invention.

In accordance with this invention the intermediate layer 16 comprises a nickel alloy having trace quantities of impurities therein and having a magnesium oxide content within the range from about 0.12 to 0.30 percent by weight dispersed therein. Preferably, for example, the layer 16 is formed of a material having a composition, by weight, of from 99.6 to 99.8 percent nickel, 0.12 to 0.30 percent magnesium oxide, 0.00] maximum percent copper, 0.005 maximum percent iron, 0.00] maximum percent manganese, 0.02 maximum percent carbon, 0.001 maximum percent silicon, 0.001 maximum percent sulfur, 0.001 maximum percent cobalt, 0.00l maximum percent chromium, and 0.00] maximum percent titanium. The abovedescribed intermediate layer 16 may be referred to as a shunt layer, since it substantially determines the resistivity of the composite thermostat metal 10.

This material of the layer 16 has a resistivity between approximately 45 ohms per circular mil foot and 50 ohms per circular mil foot and has a substantially constant deformation resistance on exposure to elevated temperatures up to approximately l000F.

As a result, the thermostat metal embodying the metal layer 16 is adapted to achieve low composite resistivity while also being adapted for use at temperatures up to about l000F. Further, because the material of the metal layer 16 does display very low resistivity despite its high temperature properties, only a very thin layer 16 is required for providing the thermostat metal 10 with a desired level of composite resistivity. Accordingly, any tendency for the metal layer 16 to reduce flexivity of the thermostat metal is minimized and, for a selected resistivity level, the thermostat metal can display improved flexivity over comparable resistivity materials of the prior art. Most important, the small thickness of the layer 16 required to provide a selected resistivity level means that only a relatively smallcontent of expensive nickel is required in the thermostat metal 10 so that the cost of the thermostat metal can be quite low. Thus, the thermostat metal of this invention achieves desired resistivity levels required for various applications while displaying improved flexivity and improved resistance to permanent deformation at elevated temperatures and further achieves these advantages at lower cost.

ln accordance with this invention, the properties of the overall composite material 10 can be varied within prescribed limits by suitable selection of the materials comprising the first and second outer layers l2, 14 as well as by varying the relative thicknesses of the respective layers so as to provide a structure having useful characteristics of resistivity and flexivity. For example, within the scope of this invention, the relative thickness of the intermediate layer 16 varies between approximately percent to 60 percent of the total thickness of the composite material, while the first outer layer varies in thickness between approximately 5 percent to 45 percent of the total thickness of the composite and the second outer layer varies in thickness between approximately 35 percent to 50 percent of the total thickness of the composite material.

In this arrangement, the thermostat metal as above-described has a relatively low composite resistivity in the range between approximately 100 ohms per circular mil foot and 400 ohms per circular mil foot and has a flexivity in the range between approximately 105 X l0- and 207 X 10 inch per inch per degreeFahrenheit.

The thermostat metal, as described hereinabove, is also characterized by suitable corrosion resistance for various widely used applications and ability to withstand elevated temperatures without deleterious effects, in particular exhibiting the property of retaining a substantially constant resistance to deformation with respect to temperature up to a temperature of approximately l000F. In addition, all of the component layers of the thermostat metal have compatible workhardening properties, and the like, so that they may be readily secured together by roll-bonding techniques, or the like, with good control of layer thickness in the resultant composite material.

Thus, an improved composite thermostat material has been described in detail hereinabove which may be seen to be characterized by useful properties in terms of flexivity and resistivity, as well as being suitable for use over a substantial temperature range.

Various changes and modifications in the abovedescribed embodiment will be readily apparent to those skilled in the art and any of such changes or modifications are deemed to be within the spirit and scope of the present invention as set forth in the appended claims.

We claim:

I. A composite thermostat material comprising a first layer ofa first metallic alloy having a relatively high CO- efficient of thermal expansion, a second outer layer of a second metallic alloy having a relatively lower coefficient of thermal expansion than said first preselected metallic alloy, and an intermediate layer comprising a nickel alloy having a magnesium oxide dispersed therein having a resistivity between approximately 45 to 50 ohms per circular mil foot and having a substantially constant resistance to deformation with respect to temperature up to a temperature of approximately l000F., said first and second outer layers being bonded to respective opposite sides of said intermediate layer.

2. A composite thermostat material as set forth in claim 1 wherein said first metallic alloy is selected from the group of alloys consisting of an alloy having a composition, by weight, of approximately 22 percent nickel, 3 percent chromium, and the balance iron, and an alloy having a composition, by weight, of 72 percent manganese, 18 percent copper, and 10 percent nickel, and wherein said second metallic alloy has a composition, by weight, of approximately 35 /2 to 36 /2 percent nickel and the balance iron.

3. A composite thermostat material as set forth in claim 2 wherein said intermediate layer is formed of nickel having trace quantities of impurities therein and having a content of magnesium oxide in the range from 0.12 to 0.30 weight percent dispersed therein.

4. A composite thermostat material as set forth in claim 3 wherein said first metal layer has a thickness comprising between approximately 5 to 45 percent of the total thickness of said composite material, said second metal layer has a thickness comprising between approximately 35 to 50 percent of the total thickness of said composite material, and said intermediate metal layer has a thickness comprising between approximately 5 to 60 percent of the total thickness of said composite material, and wherein said composite material has a flexivity of between 105 X l0 to 207 X 10 inch per inch per degree Fahrenheit and a resistivity of between approximately to 400 ohms per circular mil foot.

5. A composite thermostat material as set forth in claim 4 wherein said intermediate metal layer is formed of an alloy having a composition, by weight, of from 99.6 to 99.8 percent nickel, 0. l2 to 0.30 percent magnesium oxide, 0.001 (max) percent copper, 0.005 (max) percent iron, 0.001 (max) percent manganese, 0.02 (max) percent carbon, 0.001 (max) percent silicon, 0.001 (max) percent sulfur, 0.001 (max) percent cobalt, 0.00] (max) percent chromium, and 0.001

(max) percent titanium. 

1. A COMPOSITE THERMOSTAT MATERIAL COMPRISING A FIRST LAYER OF A FIRST METALLIC ALLOY HAVING A RELATIVELY HIGH COEFFICIENT OF THERMAL EXPANSION, A SECOND OUTER LAYER OF A SECOND METALLIC ALLOY HAVING A RELATIVELY LOWER COEFFICIENT OF THERMAL EXPANSION THAN SAID FIRST PRESELECTED METALLIC ALLOY, AND AN INTERMEDIATE LAYER COMPRISNG A NICKEL ALLOY HAVING A MAGNESIUM OXIDE DISPERSED THEREIN HAVING A RESISTIVIEY BETWEEN APPROXIMATELY 45 TO 50 OHMS PER CIRCULAR MIL FOOT AND HAVING A SUB STANTIALLY CONSTANT RESISTANCE TO DEFORMATION WITH RESPECT TO TEMPERATURE UP TO A TEMPERATURE OF APPROXIMATELY 1000*F, SAID FIRST AND SECOND OUTER LAYERS BEING BONDED TO RESPECTIVE OPPOSITE SIDES OF SAID INTERMDATE LAYER.
 2. A composite thermostat material as set forth in claim 1 wherein said first metallic alloy is selected from the group of alloys consisting of an alloy having a composition, by weight, of approximately 22 percent nickel, 3 percent chromium, and the balance iron, and an alloy having a composition, by weight, of 72 percent manganese, 18 percent copper, and 10 percent nickel, and wherein said second metallic alloy has a composition, by weight, of approximately 35 1/2 to 36 1/2 percent nickel and the balance iron.
 3. A composite thermostat material as set forth in claim 2 wherein said intermediate layer is formed of nickel having trace quantities of impurities therein and having a content of magnesium oxide in the range from 0.12 to 0.30 weight percent dispersed therein.
 4. A composite thermostat material as set forth in claim 3 wherein said first metal layer has a thickness comprising between approximately 5 to 45 percent of the total thickness of said composite material, said second metal layer has a thickness comprising between approximately 35 to 50 percent of the total thickness of said composite material, and said intermediate metal layer has a thickness comprising between approximately 5 to 60 percent of the total thickness of said composite material, and wherein said composite material has a flexivity of between 105 X 10 7 to 207 X 10 7 inch per inch per degree Fahrenheit and a resistivity of between approximately 100 to 400 ohms per circular mil foot.
 5. A composite thermostat material as set forth in claim 4 wherein said intermediate metal layer is formed of an alloy having a composition, by weight, of from 99.6 to 99.8 percent nickel, 0.12 to 0.30 percent magnesium oxide, 0.001 (max) percent copper, 0.005 (max) percent iron, 0.001 (max) percent manganese, 0.02 (max) percent carbon, 0.001 (max) percent silicon, 0.001 (max) percent sulfur, 0.001 (max) percent cobalt, 0.001 (max) percent chromium, and 0.001 (max) percent titanium. 